1. Field of the Invention
This invention relates to new and useful improvements in safety equipment for the protection of an apparatus from exceeding its safe operating temperature range, and more particularly to safety equipment which is simple, passive, extremely reliable, and does not release the contents of the apparatus to the atmosphere.
2. Brief Description of the Prior Art
It is well known that when heat is added to and removed from an apparatus the amount of heat removed and the amount of heat added must be precisely the same amount or the temperature of the equipment will eventually exceed either its maximum safe working temperature or its minimum safe working temperature. Instruments and controllers in various degrees of sophistication are added to the apparatus depending on the complexity of the apparatus. Redundant controls are added to very critical types of apparatus. Whenever possible a passive safety device is installed for the eventuality that the control system fails. When the contents of an apparatus can be vented to the atmosphere a safety valve may be used to vent the contents of the apparatus directly to the atmosphere, or indirectly by venting the contents through a flare system. When it is uneconomical or environmentally unacceptable to vent the contents of an apparatus to the atmosphere a passive safety system is more difficult to design, and in the case of atomic power plants a design for a passive safety system has not been realized.
The simplicity and reliability of the passive heat pipe has been recognized. This apparatus was chosen to maintain the permafrost under the Alaskan pipeline. Its reliability has been proposed as a way of eliminating some of the redundancy in atomic power plants.
Burelbach et al U.S. Pat. No. 4,478,784 discloses the use of a heat pipe for maintaining adjacent or related components of a nuclear reactor within specified temperature differences.
Huebotter et al U.S. Pat. No. 4,560,533 discloses the use of heat pipe exchangers to transfer energy from the primary coolant to the steam/water coolant system of an atomic power plant.
Neider et al U.S. Pat. No. 4,727,455 discloses a semiconductor power module with an integrated heat pipe for regulating temperature.
The reliability of the heat pipe results since only gravity or capillary action in a wick is necessary for the heat pipe to function. Conventional two-phase heat pipes located in the vertical position use gravity for working fluid circulation and comprise a vertical pipe containing liquid which is vaporized from the bottom end and flows as a vapor to the upper end where the vapors condense and flow by gravity back to the bottom end. Heat pipes which must transfer heat horizontally use capillary action in wicks for working fluid circulation. In horizontal heat pipes, capillary wicks transfer liquid from one end of the pipe where the vapors condense to the other end where the liquid is vaporized.
The simplicity of the heat pipe results from its construction, which may be as simple as only a sealed tube partially filled with a liquid. Various extended surface designs may be used externally to increase the capacity of an individual pipe. Internals may also be used to increase the capacity of a pipe. Heat exchanger bundles are made by installing parallel pipes. The interior volume may be tied together, or they may be individually sealed so that the failure of one pipe will not affect the performance of the remaining pipes.
The operation and construction of two phase heat pipes are well known, and these construction techniques will be used in the design of the three phase heat pipe which constitutes this invention. They are not a part of this invention but will be discussed briefly below.